In the 7th chapter, namely Operation, Administration and Maintenance (OAM), of the Broadband Forum (BBF) standard TR101, a method for maintaining the access network based on the Ethernet is defined. In the definition of the chapter, based on the method of the IEEE Standard 802.1ag, four layers of administration domains, respectively Customer, Carrier, Intra-Carrier and Access Link, are defined in combination with the actual condition of the access network. In each domain, the Maintenance End Point (MEP) function is implemented between the two end points, and the Maintenance Intermediate Point (MIP) function is implemented in the middle of the link. Between the MEP node and the MIP node, the Ethernet OAM message is sent, forwarded and replied to help localize the specific area of the Ethernet breakdown.
The main function of the 4 administration domains defined in the standard is providing the operator with an end-to-end method at the Ethernet level, to help the operator to diagnose and locate the link fault. Since the existing access technology is mainly the Digital Subscriber Line (DSL) technology, the Access Node is mainly an independent Digital Subscriber Line Access Multiplexer (DSLAM). After introducing the PON technology into the access network, an originally independent access node has been expanded as a network consisting of the OLT, the ONU and an Optical Distribution Network (ODN).
Therefore, according to the existing Ethernet Passive Optical Network (EPON) described in Standard TR101, IEEE 802.3ah standard provides a simple method (namely, loop-back and bit error rate detection) for diagnosing the physical layer fault between the OLT and the ONU, while there is no specific maintenance and administration method at the Ethernet level whose level is higher than the physical layer optical link.